Exploring phenotypic and genetic variability in hemp (Cannabis sativa)

Hemp (Cannabis sativa L.) is a high-value multi-purpose crop with applications ranging from the medicinal use of its secondary metabolites to carbon-sequestering building materials. To fully capitalise on the potential of hemp as a crop for more sustainable agriculture, detailed phenotypic and genotypic characterizations are required in order to inform targeted breeding programmes. Here, we present a detailed morphological and genomic analysis of 10 hemp cultivars. We found high variability in agronomically important traits such as flowering time, plant height, and biomass in most of the hemp cultivars tested. Additionally, genotyping by sequencing demonstrates that genetic differences are pervasive, both between hemp cultivars as well as between individuals of a single cultivar. The significant genetic and phenotypic variability we observe in hemp contrasts with other crops, where cultivars are often phenotypically and genetically relatively uniform. We argue that the variability of hemp is an asset for breeding and increases the potential for further improvement of the crop but is also a challenge for todays highly automated agriculture that relies on phenotypic uniformity. Author summaryHemp (Cannabis sativa L.) stands as one of the earliest domesticated crops. This remarkable plant is a sustainable crop with high carbon sequestration capacity which can be cultivated for soil remediation. Furthermore, hemp oil and fibre are used for many applications ranging from cooking to manufacturing bioplastics, textiles, or building materials of superb characteristics, and its secondary metabolites are sought after because of their medicinal properties. However, in contrast to many modern crops, hemp exhibits extensive variability in key agricultural traits, such as plant height and flowering time. This variability presents a challenge for both farmers and processors. To unravel the fundamentals of hemp diversity we conducted a comprehensive study of phenotypic and genetic characterisation of ten diverse hemp cultivars. We present findings confirming substantial variability not only among individuals of different cultivars but also within the same cultivar. Additionally, we explore heterozygosity in the context of other hemp studies and other crops. Understanding this variability in the context of a single hemp cultivar and across multiple cultivars is paramount for breeding novel, more uniform hemp varieties which will allow us to unlock the full potential of hemp as a crop of the future.